CN112683942A - Diaphragm thermal shrinkage assessment method - Google Patents

Diaphragm thermal shrinkage assessment method Download PDF

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Publication number
CN112683942A
CN112683942A CN202011565433.3A CN202011565433A CN112683942A CN 112683942 A CN112683942 A CN 112683942A CN 202011565433 A CN202011565433 A CN 202011565433A CN 112683942 A CN112683942 A CN 112683942A
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Prior art keywords
diaphragm
longitudinal
shrinkage
separator
area
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Inventor
徐嘉辉
陈辉
李叶珠
李欣
夏小勇
陶德瑜
于紫阳
张燕萍
楚英
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Dongguan Weike Battery Co ltd
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Dongguan Weike Battery Co ltd
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Abstract

The invention relates to a diaphragm thermal shrinkage evaluation method, which comprises the following steps: taking a diaphragm to be measured, making a cross mark on the diaphragm, wherein the cross mark comprises a transverse line and a longitudinal line, and measuring the original lengths of the transverse line and the longitudinal line; winding the diaphragm with the cross mark, the positive plate and the negative plate into a battery cell, wherein the diaphragm is positioned between the positive plate and the negative plate; placing the battery core at a specified test temperature, keeping the temperature constant for a certain time, taking out the battery core, disassembling the battery core, and taking out the diaphragm for evaluation; measuring the lengths of a transverse line and a longitudinal line after the cross mark on the diaphragm is cooled to room temperature, calculating the transverse shrinkage rate and the longitudinal shrinkage rate of the diaphragm, measuring and calculating the approximate area of an arc-shaped shrinkage area at the edge of the diaphragm, and calculating the ratio of the approximate area to the winding single-fold area of the diaphragm; and (4) taking the longitudinal shrinkage rate and the area ratio as evaluation indexes to evaluate the safety risk level of the diaphragm to be tested. Compared with the prior art, the evaluation method provided by the invention has the advantage that the accuracy and operability of the thermal shrinkage evaluation of the diaphragm are improved.

Description

Diaphragm thermal shrinkage assessment method
Technical Field
The invention belongs to the technical field of diaphragms, and particularly relates to a diaphragm thermal shrinkage evaluation method.
Background
After the 21 st century, lithium ion batteries have been greatly improved in terms of energy density, rate, cycle life, and the like, and are spread over various fields of life, and particularly, 3C products have become an indispensable tool in life. As a main power supply scheme of 3C products, the safety of lithium ion batteries is always a key factor of consumer attention.
The diaphragm is one of four main materials of the lithium battery, and has the main function of separating the positive electrode and the negative electrode of the battery, preventing the two electrodes from contacting and short-circuiting, avoiding the thermal runaway ignition in the battery, so that the performance of the diaphragm has great influence on the safety of the battery core. The demand for battery light weight and high capacity in the 3C industry is currently increasing in the demand for separator performance at the design end of lithium batteries. Therefore, a method for evaluating the properties of the separator, particularly the thermodynamic properties, is essential.
Based on the winding structure of the current lithium ion battery, the positive and negative pole pieces are separated by the diaphragm, the length of the diaphragm in the width direction is greater than that of the pole pieces, and the pole pieces at the center of the winding structure are connected with the pole lugs. Due to the complexity of the winding structure, when the winding core is heated, the heat concentration conditions at all positions of the winding core are not consistent, and the heating conditions of the internal diaphragm are also not consistent, so that the heat shrinkage condition of the diaphragm in the state is different from that in the natural stretching condition of the diaphragm. However, the current thermodynamic test method for the separator usually only tests the thermal shrinkage condition of the separator under the natural stretching condition, that is, certain errors exist in evaluating the thermal safety of the separator applied to the lithium ion battery by using the shrinkage data.
In view of the above, there is a need to provide a new method for evaluating thermal shrinkage of a separator, so as to accurately and effectively evaluate the thermal shrinkage of the separator in a flexible package cell.
Disclosure of Invention
The invention aims to: aiming at the defects of the prior art, the diaphragm thermal shrinkage evaluation method is provided, and the accuracy and operability of the diaphragm thermal shrinkage evaluation are improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for evaluating thermal shrinkage of a separator, comprising the steps of:
1) taking a diaphragm to be measured, making a cross mark on the diaphragm, wherein the cross mark comprises a transverse line and a longitudinal line, and measuring the original length X of the transverse line and the longitudinal line1And Y1
2) Winding the diaphragm to be tested with the cross mark, the positive plate and the negative plate into a battery cell, wherein the diaphragm is positioned between the positive plate and the negative plate;
3) placing the wound battery core at a specified test temperature for a certain time, taking out, disassembling, and taking out the diaphragm for evaluation;
4) measuring the length X of the transverse line and the longitudinal line after the cross mark on the diaphragm is cooled to room temperature2And Y2Calculating the transverse shrinkage (X) of the separator1-X2)/X1And longitudinal shrinkage (Y)1-Y2)/Y1Simultaneously measuring and calculating the approximate area S of the circular arc retraction area of the edge of the diaphragm1Calculating an approximate area S1Ratio S to the winding area S of the separator1/S;
5) And (4) taking the longitudinal shrinkage rate and the area ratio as evaluation indexes to evaluate the safety risk level of the diaphragm to be tested.
As an improvement of the method for evaluating the thermal shrinkage of the diaphragm, in the step 1), when cross marks are made on the diaphragm to be measured, the cross marks are uniformly distributed in the length direction and the width direction of the diaphragm.
As an improvement of the method for evaluating the thermal shrinkage of the diaphragm, in the step 4), the approximate area S of the circular arc shrinkage area of the edge of the diaphragm1And 1/2XY, wherein X is the transverse length of the arc run-in region and Y is the longitudinal maximum height of the arc run-in region.
As an improvement of the method for evaluating the thermal shrinkage of the separator according to the present invention, in step 5), the following values are specifically counted during evaluation: the number of longitudinal shrinkage rates of 3 to 5% and more than 5%, respectively, and the number of area ratios of 3 to 5% and more than 5%, respectively.
As an improvement of the membrane thermal contraction assessment method, the safety risk grades are divided into five grades of high risk, higher risk, middle risk, lower risk and low risk.
As an improvement of the thermal shrinkage evaluation method of the diaphragm, when the number of longitudinal shrinkage rates larger than 5% and the number of area ratios larger than 5% are both larger than 0, the diaphragm is evaluated to be at high risk.
As an improvement of the method for evaluating thermal shrinkage of a separator according to the present invention, when one of the number of longitudinal shrinkage rates greater than 5% and the number of area ratios greater than 5% is greater than 0, the separator is evaluated as a higher risk.
As an improvement of the thermal shrinkage evaluation method of the diaphragm, when the number of longitudinal shrinkage rates larger than 5% and the number of area ratios larger than 5% are both smaller than 1, and the number of longitudinal shrinkage rates of 3-5% and the number of area ratios of 3-5% are both larger than 1, the measured diaphragm is evaluated as medium risk.
As an improvement of the thermal shrinkage evaluation method of the diaphragm, when the number of longitudinal shrinkage rates larger than 5% and the number of area ratios larger than 5% are both smaller than 1, and one of the number of longitudinal shrinkage rates of 3-5% and the number of area ratios of 3-5% is larger than 1, the measured diaphragm is evaluated to be at a lower risk.
As an improvement of the thermal shrinkage evaluation method of the diaphragm, when the number of longitudinal shrinkage rates larger than 5%, the number of area ratios larger than 5%, the number of longitudinal shrinkage rates of 3-5% and the number of area ratios of 3-5% are all smaller than 1, the evaluation of the diaphragm is low risk.
Compared with the prior art, the invention has the beneficial effects that: the invention provides a diaphragm thermal shrinkage evaluation method, which is used for simulating the actual state of a diaphragm in a soft-package battery cell and testing by adopting an uncharged winding battery cell which is not injected with liquid.
Drawings
FIG. 1 is a schematic diagram of a cross mark made on a membrane to be measured.
Fig. 2 is a schematic structural diagram of a winding core in the embodiment.
FIG. 3 is a schematic view of the circular arc receding area of the edge of the membrane and the membrane winding single-fold structure in the example.
Fig. 4 is a structural view showing the expansion of the diaphragm in the embodiment.
Detailed Description
The present invention will be described in further detail below, but the embodiments of the present invention are not limited thereto.
The invention provides a diaphragm thermal shrinkage evaluation method, which comprises the following steps:
1) taking a diaphragm to be measured, making cross marks on the diaphragm, wherein the cross marks are uniformly distributed in the length direction and the width direction of the diaphragm, each cross mark comprises a transverse line and a longitudinal line, and measuring the original length X of the transverse line and the original length X of the longitudinal line1And Y1
2) Winding the diaphragm to be tested with the cross mark, the positive plate and the negative plate into a battery cell, wherein the diaphragm is positioned between the positive plate and the negative plate;
3) placing the wound battery core at a specified test temperature for a certain time, taking out, disassembling, and taking out the diaphragm for evaluation;
4) measuring the length X of the transverse line and the longitudinal line after the cross mark on the diaphragm is cooled to room temperature1And Y1Calculating the transverse shrinkage (X) of the separator1-X2)/X1And longitudinal shrinkage (Y)1-Y2)/Y1Simultaneously measuring and calculating the approximate area S of the circular arc retraction area of the edge of the diaphragm1Approximate area S of the circular arc retraction area of the diaphragm edge11/2XY, wherein X is the transverse length of the arc retraction area, and Y is the longitudinal maximum height of the arc retraction area; finally calculating the approximate area S1Ratio S to the winding area S of the separator1/S;
5) And (4) taking the longitudinal shrinkage rate and the area ratio as evaluation indexes to evaluate the safety risk level of the diaphragm to be tested. The following values were counted specifically at the time of evaluation: the number of longitudinal shrinkage rates of 3 to 5% and more than 5%, respectively, and the number of area ratios of 3 to 5% and more than 5%, respectively. The safety risk levels are divided into five levels of high risk, higher risk, medium risk, lower risk and low risk.
The specific evaluation criteria are as follows:
when the number of longitudinal shrinkage rates greater than 5% and the number of area ratios greater than 5% are both greater than 0, the measured diaphragm is evaluated as high risk;
when one of the number of longitudinal shrinkage rates greater than 5% and the number of area ratios greater than 5% is greater than 0, the measured diaphragm is evaluated as a higher risk;
when the number of longitudinal shrinkage rates larger than 5% and the number of area ratios larger than 5% are both smaller than 1, and the number of longitudinal shrinkage rates of 3-5% and the number of area ratios of 3-5% are both larger than 1, the measured diaphragm is evaluated as a medium risk;
when the number of longitudinal shrinkage rates larger than 5% and the number of area ratios larger than 5% are both smaller than 1, and one of the number of longitudinal shrinkage rates of 3-5% and the number of area ratios of 3-5% is larger than 1, the measured diaphragm is evaluated as a low risk;
and when the number of longitudinal shrinkage rates larger than 5%, the number of area ratios larger than 5%, the number of longitudinal shrinkage rates of 3-5% and the number of area ratios of 3-5% are all smaller than 1, evaluating the membrane to be low risk.
Embodiments of the present invention are illustrated below with reference to examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the claimed invention.
Examples
A method for evaluating thermal shrinkage of a separator, comprising the steps of:
1) taking a diaphragm to be measured, as shown in figure 1, making cross marks on the diaphragm, wherein the cross marks are uniformly distributed in the length direction and the width direction of the diaphragm, each cross mark comprises a transverse line and a longitudinal line, and measuring the original length X of the transverse line and the longitudinal line1And Y1
2) Winding the diaphragm to be tested with the cross mark, the positive plate and the negative plate into a battery cell as shown in figure 2, wherein the diaphragm is positioned between the positive plate and the negative plate;
3) placing the wound battery cell at 130 ℃ and keeping the temperature for 0.5h, 1h, 2h and 6h respectively, then taking out, disassembling, and taking out the diaphragm for evaluation;
4) measuring the length X of the transverse line and the longitudinal line after the cross mark on the diaphragm is cooled to room temperature2And Y2Calculating the transverse shrinkage (X) of the separator1-X2)/X1And longitudinal shrinkage (Y)1-Y2)/Y1Simultaneously measuring and calculating the approximate area S of the circular arc retraction area of the edge of the diaphragm1As shown in fig. 3, the approximate area S of the circular arc receding region of the diaphragm edge11/2XY, wherein X is the transverse length of the arc retraction area, and Y is the longitudinal maximum height of the arc retraction area; finally calculating the approximate area S1Ratio S to the winding area S of the separator1/S;
5) And counting the number of longitudinal shrinkage rates of 3-5% and more than 5% respectively, and the number of area ratios of 3-5% and more than 5% respectively, and evaluating the safety risk level of the diaphragm to be tested by taking the numbers as evaluation indexes.
In the above evaluation, the transverse direction is the winding direction of the separator, and the longitudinal direction is perpendicular to the winding direction of the separator.
Comparative example
A method for evaluating thermal shrinkage of a separator, comprising the steps of:
1) taking a diaphragm to be measured, as shown in figure 1, making cross marks on the diaphragm, wherein the cross marks are uniformly distributed in the length direction and the width direction of the diaphragm, each cross mark comprises a transverse line and a longitudinal line, and measuring the original length X of the transverse line and the longitudinal line1And Y1
2) As shown in fig. 4, the membrane to be measured with the cross mark is placed at a constant temperature of 130 ℃ for 0.5h, 1h, 2h and 6h in an unfolded state, and then taken out for evaluation;
4) measuring the length X of the transverse line and the longitudinal line after the cross mark on the diaphragm is cooled to room temperature2And Y2Calculating the transverse shrinkage rate (X-X) of the diaphragm1) X and longitudinal shrinkage (Y-Y)1)/Y。
Evaluation results
1. Two sheets of the same separator having the same dimensions as the batch were evaluated by the method of example, and by the method of comparative example, and the measured transverse shrinkage and longitudinal shrinkage were as shown in table 1.
Table 1 transverse shrinkage and longitudinal shrinkage of the separator
Figure BDA0002860492060000061
2. The evaluation was carried out by taking 3 different kinds of separators and by using the methods of examples, respectively, and the results are shown in table 2.
TABLE 2 evaluation results
Figure BDA0002860492060000062
From the above test evaluation results, it can be seen that:
1) the evaluation method of the thermal shrinkage of the diaphragm in the comparative example is to test the average shrinkage rate of the diaphragm in the transverse and longitudinal directions before and after heat treatment after the stretched diaphragm is placed at a high temperature for a certain time for heat preservation, and the evaluation method is different from the evaluation method of the invention in the result, on one hand, the diaphragm is subjected to different tensile forces in the transverse and longitudinal directions under the winding state of a battery cell, and whether the stress of the diaphragm at the softening temperature of the diaphragm greatly affects the shrinkage of the diaphragm; on the other hand, the difference in thermal conductivity at the metal tabs in the wound structure will result in a faster local temperature rise of the separator, resulting in a greater contraction in local areas than in other areas. The above is not considered by the comparative example.
2) According to the invention, the relevant numerical values obtained by measurement and calculation are counted, the ratio of the longitudinal shrinkage rate and the approximate area of the arc shrinkage area of the edge of the diaphragm to the winding single-fold area of the diaphragm is used as an evaluation index, a proper evaluation standard is determined, the thermal shrinkage and the safety of the diaphragm are evaluated in a grade manner, and the accuracy is higher.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (10)

1. A method for evaluating thermal shrinkage of a separator, comprising the steps of:
1) taking a diaphragm to be measured, making a cross mark on the diaphragm, wherein the cross mark comprises a transverse line and a longitudinal line, and measuring the original length X of the transverse line and the longitudinal line1And Y1
2) Winding the diaphragm to be tested with the cross mark, the positive plate and the negative plate into a battery cell, wherein the diaphragm is positioned between the positive plate and the negative plate;
3) placing the wound battery core at a specified test temperature for a certain time, taking out, disassembling, and taking out the diaphragm for evaluation;
4) measuring the length X of the transverse line and the longitudinal line after the cross mark on the diaphragm is cooled to room temperature2And Y2Calculating the transverse shrinkage (X) of the separator1-X2)/X1And longitudinal shrinkage (Y)1-Y2)/Y1Simultaneously measuring and calculating the approximate area S of the circular arc retraction area of the edge of the diaphragm1Calculating an approximate area S1Ratio S to the winding area S of the separator1/S;
5) And (4) taking the longitudinal shrinkage rate and the area ratio as evaluation indexes to evaluate the safety risk level of the diaphragm to be tested.
2. The method for evaluating thermal shrinkage of a separator according to claim 1, wherein in step 1), when the cross marks are made on the separator to be measured, the cross marks are uniformly distributed in the length direction and the width direction of the separator.
3. The method for evaluating thermal shrinkage of a separator according to claim 1, wherein in step 4), the approximate area S of the circular arc shrinking region of the edge of the separator is1And 1/2XY, wherein X is the transverse length of the arc run-in region and Y is the longitudinal maximum height of the arc run-in region.
4. The method for evaluating thermal shrinkage of a separator according to claim 1, wherein in step 5), the following values are counted: the number of longitudinal shrinkage rates of 3 to 5% and more than 5%, respectively, and the number of area ratios of 3 to 5% and more than 5%, respectively.
5. The membrane thermal contraction assessment method according to claim 1, wherein the safety risk levels are classified into five levels of high risk, higher risk, medium risk, lower risk, and low risk.
6. The method for evaluating thermal shrinkage of a separator according to claim 1, wherein the measured separator is evaluated as high risk when both the number of longitudinal shrinkage rates greater than 5% and the number of area ratios greater than 5% are greater than 0.
7. The method for evaluating thermal shrinkage of a separator according to claim 1, wherein the measured separator is evaluated as higher risk when one of the number of longitudinal shrinkage rates greater than 5% and the number of area ratios greater than 5% is greater than 0.
8. The method for evaluating thermal shrinkage of a separator according to claim 1, wherein the measured separator is evaluated as medium risk when the number of longitudinal shrinkage rates greater than 5% and the number of area ratios greater than 5% are both less than 1, and the number of longitudinal shrinkage rates of 3 to 5% and the number of area ratios of 3 to 5% are both greater than 1.
9. The method for evaluating thermal shrinkage of a separator according to claim 1, wherein the measured separator is evaluated as low risk when both the number of longitudinal shrinkage ratios of greater than 5% and the number of area ratios of greater than 5% are less than 1, and one of the number of longitudinal shrinkage ratios of 3 to 5% and the number of area ratios of 3 to 5% is greater than 1.
10. The method for evaluating thermal shrinkage of a separator according to claim 1, wherein the measured separator is evaluated as low risk when the number of longitudinal shrinkage ratios of more than 5%, the number of area ratios of more than 5%, the number of longitudinal shrinkage ratios of 3 to 5%, and the number of area ratios of 3 to 5% are all less than 1.
CN202011565433.3A 2020-12-25 2020-12-25 Diaphragm thermal shrinkage assessment method Pending CN112683942A (en)

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Citations (8)

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Publication number Priority date Publication date Assignee Title
CN101276943A (en) * 2007-02-06 2008-10-01 松下电器产业株式会社 Evaluation method and evaluation apparatus for evaluating battery safety and battery
CN101587045A (en) * 2008-05-23 2009-11-25 比亚迪股份有限公司 Method for evaluating brittle damage of electrode slice of lithium ion battery
CN103308548A (en) * 2013-07-06 2013-09-18 国家烟草质量监督检验中心 Measuring method of thermal shrinkage rate of cigarette packaging film
CN106855525A (en) * 2016-12-27 2017-06-16 深圳市星源材质科技股份有限公司 A kind of method for testing barrier film high temperature percent thermal shrinkage
CN108195677A (en) * 2018-02-01 2018-06-22 中航锂电(洛阳)有限公司 A kind of battery pole piece flexibility detection method
CN109781775A (en) * 2018-12-10 2019-05-21 深圳市比克动力电池有限公司 The measurement method of lithium ion battery separator shrinking percentage
KR20200073818A (en) * 2018-12-14 2020-06-24 주식회사 포스코 Specimen measuring apparatus and method
CN211697212U (en) * 2019-12-12 2020-10-16 国联汽车动力电池研究院有限责任公司 Performance testing device for battery diaphragm

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101276943A (en) * 2007-02-06 2008-10-01 松下电器产业株式会社 Evaluation method and evaluation apparatus for evaluating battery safety and battery
CN101587045A (en) * 2008-05-23 2009-11-25 比亚迪股份有限公司 Method for evaluating brittle damage of electrode slice of lithium ion battery
CN103308548A (en) * 2013-07-06 2013-09-18 国家烟草质量监督检验中心 Measuring method of thermal shrinkage rate of cigarette packaging film
CN106855525A (en) * 2016-12-27 2017-06-16 深圳市星源材质科技股份有限公司 A kind of method for testing barrier film high temperature percent thermal shrinkage
CN108195677A (en) * 2018-02-01 2018-06-22 中航锂电(洛阳)有限公司 A kind of battery pole piece flexibility detection method
CN109781775A (en) * 2018-12-10 2019-05-21 深圳市比克动力电池有限公司 The measurement method of lithium ion battery separator shrinking percentage
KR20200073818A (en) * 2018-12-14 2020-06-24 주식회사 포스코 Specimen measuring apparatus and method
CN211697212U (en) * 2019-12-12 2020-10-16 国联汽车动力电池研究院有限责任公司 Performance testing device for battery diaphragm

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Application publication date: 20210420